"If you are a developer, I expect you to be very competent."
You don't expect other people you work with to be equally competent?
Maybe you wrote it this way because you find other competencies harder to evaluate. If that's the case, try the "animal test": http://www.paulgraham.com/start.html
Exactly. There is no point in expecting cofounder to be competent in same areas. What is more important for cofounder is share same passion as you do. Technical stuff can be learned. Languages and technology comes and goes.
You don't expect other people you work with to be equally competent?
Maybe you wrote it this way because you find other competencies harder to evaluate. If that's the case, try the "animal test": http://www.paulgraham.com/start.html